We investigate the characteristics of single-crystallike (SCL) poly-Si nanowire (SCL poly-Si NW) thin-filmtransistors with gate-all-around (GAA) structures. The GAA SCL poly-Si NWs are prepared by a modified sidewall spacer process utilizing an amorphous silicon (α-Si) mesa structure. The combination of the high surface-to-volume ratio of the NW and a nominal gate length of 0.25 μm lead to clear improvement in electrical performance, including a steep subthreshold swing (90 ± 15 mV/dec), a virtual absence of drain-induced barrier lowering (21 ± 13 mV/V), and a very high ON/OFF current ratio ∼7 × 10^7 (VD = 1 V, VG = 3 V). [IEEE Electron Device Letters, 34(4), 523-525, 2013]
2. Nanobelt Field Effect Transistor with Extended Gate for Use as a Biosensor
In this study, various types of extended gate field effect transistor (EGFET) biosensors were compared and then a model based on potential coupling between a disposable extended gate (EG) capacitor and the gate–source/drain capacitor of a nanobelt field effect transistor (NBFET) was developed and optimized for biosensor applications. Several parameters, including the dielectric thicknesses and the EG gate area coverage, the ionic strength of buffer solution, and the charge density of specific binding biomolecules, were included in the model. The potential coupling efficiency between the potential induced by surface charge on the EG and the gate voltage of the FET was analyzed and verified through pH detection. Biotin–streptavidin/avidin sensing was demonstrated with the optimized EG and NBFET. In addition, real-time measurements of the detection of botulinum neural toxin (BoNT) type-A were also performed using the EG NBFET, which could detect an extremely low concentration (20 fM) of BoNT type-A. Because the nanoelectronic field effect transistor does not need to be sacrificed after detection, the optimized EG NBFET biosensor has great potential for use in bio/chemical and point-of-care applications. [ECS Journal of Solid State Science and Technology, 7(7), Q3172-Q3179, 2018]
3. Selective Deposition of Multiple Sensing Materials on Si Nanobelt Devices
This paper describes a novel method, using device-localized Joule heating (JH) in a plasma enhanced atomic layer deposition (PEALD) system, for the selective deposition of platinum (Pt) and zinc oxide (ZnO) in the n− regions of n+/n−/n+ polysilicon nanobelts (SNBs). COMSOL simulations were adopted to estimate device temperature distribution. However, during ALD process, the resistance of SNB device decreased gradually and reached to minima after 20 min JH. As a result, thermal decomposition of precursors occurred during PEALD process. Selective deposition in the n− region was dominated by CVD instead of ALD. Selective deposition of Pt and ZnO films has been achieved and characterized using atomic force microscopy, scanning electron microscopy, and transmission electron microscopy. [ACS Applied Materials & Interfaces, 9(46), 39935-39939, 2017]
4. Hydrogen Gas Sensors from Polysilicon Nanobelt Devices
Double-junction n+/n– /n+ polysilicon nanobelts featuring selectively deposited sensing materials have been investigated for application as H2 gas sensors. The selective modification of the devices was performed through a combination of localized ablation of a resist and lift-off of a previous catalyst material deposited through e-beam evaporation. Four nanobelt devices, differentiated by their doping concentrations at the n– region (from 2.5 × 10^13 to 2.5 × 10^14 cm^−2 ), were analyzed in terms of the responses to H2 and their self-heating effects. A low doping concentration improved the response at room temperature, owing to a longer Debye length. The variation in the H2-induced surface potential associated with temperature, accounting for degradation in the response of the nanobelts with Joule heating bias, was analyzed in terms of the I–V characteristics of the double-junction device. Among various catalysts (Pt, Pd, Pt/Pd) evaluated for their H2 sensing characteristics, an ultrathin film of Pt/Pd was most favorable. [Nanotechnology, 27(50), 505604,2016]